Syringes typically each comprise a barrel having a through opening including a cylindrical portion; a plunger adapted to be inserted into the cylindrical portion of the opening and having a groove around its periphery; and a resiliently elastic O-ring within the groove around the plunger, which O-ring has a circular cross section with a predetermined diameter adapted to be compressed between the plunger and the cylindrical inner surface of the syringe to provide a seal therebetween.
A problem exists in removing air from between the plunger and material (e.g., a liquid or paste) within the opening in the barrel when the syringe is assembled such as at a factory or by a user of the syringe. Various plunger structures have been suggested to vent this air when the plunger is inserted (see U.S. Pat. Nos. 3,674,181; 4,340,067 and 4,405,249). These structures, however, are not useful for many materials so that some persons filling syringes have resorted to filling them under vacuum conditions, which is both expensive and time consuming.